It is well known that progressively more apparatuses are being assembled by means of threaded assemblies such as bolts, nuts, etc.; and that in assemblying larger devices, such as automobiles and the like, the amount of tightening these threaded assemblies is often very critical. For example, if a bolt is tightened to too great an extent, the bolt will be stretched; so that its desired strength is not available. On the other hand, if the bolt is not tightened sufficiently, there is a danger of its loosening to the point at which it may actually fall off. In fact, it appears that government specifications and the danger of law suits may cause the recall of many vehicles for readjustment of threaded assemblies.
In the past, the tightening of threaded assemblies was accomplished manually, the amount of tightening being left to the individual operator; but variations in strength, attitude, judgment, etc.-- and the need for mass production soon obsoleted this manual procedure. Soon after this, power wrenches were introduced; these comprising motors that were driven electrically, pneumatically, or hydraulically. The wrench motors are suitably geared to provide the desired rotational speed and "torque" (which is a measure of the turning strength of the wrench). Moreover, most of these power wrenches contain some type of clutch that releases automatically when the bolt or nut has been suitably tightened. Unfortunately, the resultant automatic power wrench was not completely satisfactory for several reasons -- including variability of the clutch release, inertial rotation after the clutch was released, difficulty of immediate power shut-off, etc. The most common wrench used in present automated assembly processes are hand-held tools employing a right-angle wrenching head.
Thus, an improved automatic power wrench is needed.